Download - Bacterial Growth & Physiology
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BACTERIAL GROWTH&PHYSIOLOGY
II MBBS
Dr Ekta Chourasia
Department of Microbiology
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Growth
It is an increase in all the cell components,which ends in multiplication of cell leading toan increase in population.
It involves - an increase in the size of thecell & an increase in the number of individual
cells.
Bacteria divide by binary fission.
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Generation time
Interval of time between two cell divisions
OR
The time required for a bacterium to giverise to 2 daughter cells under optimumconditions
Also called population doubling time.
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Generation time
Coliform bacilli like E.coli& other medicallyimportant bacteria 20 mins
Tubercle bacilli 20 hrs
Lepra bacilli 20 days
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Growth form in Laboratory
Colonyformed by bacteria growing on solidmedia. (20-30 cell divisions)
Each bacterial colony represents a clone ofcells derived from a single parent cell.
Turbidityliquid media
- 107-109cells/ml
Biofilm formation thin spread over an inertsurface.
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Bacterial counts
Growth in numbers can be studied bybacterial counts.
2 methods Total cell count
- Viable cell count
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Total Count
Total number of cells in the sample living+ dead.
Can be obtained by :1. Direct counting under microscope using
counting chambers.
2. Counting in an electronic device Coultercounter.
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Total Count
Can be obtained by :
3. Direct counting using stained smears - byspreading a known volume of culture over a
measured area of slide.
4. Opacity measurements using an
absorptiometer/ nephalometer.
5. Chemical assaysof cell components.
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Viable Cell Count
Measures the number of living cells.
Methods
Surface colony count1. Dilution method
2. Plating method
Number of colonies that develop afterincubation gives an estimate of the viablecount.
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Bacterial Growth Curve
When a bacterium is added to a suitableliquid medium & incubated, its growthfollows a definite course.
If bacteria counts are made at intervalsafter inoculation & plotted in relation totime, a growth curve is obtained.
Shows 4 phases : Lag, Log or Exponential,Stationary & phase of Decline.
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Phases of Growth Curve
Lag phaseNo increase in number but theremay be an increase in the size of the cell.
Log OR Exponential phase cells startdividing and their number increases
exponentially.
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Phases of Growth Curve
Stationary phasecell division stops due todepletion of nutrients & accumulation oftoxic products.- equilibrium exists between dying cells andthe newly formed cells, so viable countremains stationary
Phase of Decline population decreases dueto the death of cells autolytic enzymes.
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Morphological & Physiological
alterations during growth Lag phasemaximum cell size towards the end
of lag phase.
Log phasesmaller cells, stain uniformly
Stationary phaseirregular staining,sporulation and production of exotoxins &antibiotics
Phase of Decline
involution forms(with ageing)
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Factors Affecting Bacterial Growth
Temperature
Atmosphere O2 & CO2
H-ion concentrationMoisture & drying
Osmotic effects
RadiationMechanical & sonic stress.
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Temperature
Vary in their temperature requirements.
Temperature range
growth does notoccur above the maximum or below theminimum.
Optimum Temperaturegrowth occursbest, 37C for most pathogenic bacteria.
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Temperature
Mesophilicgrows best between 25C and40C.e.g. most bacterial pathogens
Psychrophilic(cold loving) grows best below20Ce.g. Flavobacterium spps
Thermophilicgrows best at high temp, 55-58Ce.g. Bacillus stereothermophilus
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Atmosphere
Depending on the O2requirement, bacteria aredivided into :1. Strict (Obligate) Aerobes require O2 for
growth e.g. Pseudomonas aeruginosa
2. Strict (Obligate) Anaerobes grow in theabsence of O2& may even die on exposure toO2 e.g. Bacteroides fragilis
3. Microaerophilicgrow best in the presence oflow oxygen levelse.g. Campylobacterspp, Helicobacterspp
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Atmosphere
4. Facultativeanaerobeaerobic but can alsogrow in the absence of O2e.g. Staphylococcus spps
5. Aerotolerant anaerobe anaerobic, buttolerates exposure to O2e.g. Clostridium perfringens
6. Capnophilic organism requires high CO2levels eg Neisseria spps
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H-ion Concentration
pH range, optimum pH
Neutral or slightly alkaline pH (7.2 7.6) majority of pathogenic bacteria grow best.
Lactobacilli
acidic pH
Vibrio choleraealkaline pH
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Moisture & Drying
Water essential ingredient of bacterialprotoplasm. Hence drying is lethal to cells.
Effect of drying varies :T.pallidumhighly sensitiveStaphylococcispstand for months
Spores resistant to dessication, maysurvive for several decades.
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Osmotic effects
More tolerant to osmotic variation due tomechanical strength of their cell walls.
Radiation X rays & gamma rays exposure lethal
Mechanical & Sonic Stress May be ruptured by mechanical stress.
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Bacterial Nutrition
Water constitutes 80% of the total weightof bacterial cells.
Proteins, polysaccharides, lipids, nucleicacids, mucopeptides & low molecular weightcompounds make up the remaining 20%.
For growth & multiplication, the minimumnutritional requirements are water, asource of carbon, a source of nitrogen &some inorganic salts.
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Classification of Bacteria Based on
Nutritional Requirement PhototrophsBacteria which derive their
energy from sunlight.
Chemotrophs Bacteria which deriveenergy from chemical reactions.
1. Organotrophs: require organic sources ofhydrogen
2. Lithotrophs: require inorganic sources ofhydrogen like NH3, H2S
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Classification of Bacteria Based on
Nutritional Requirement Based on the utilization of carbon
compounds, bacteria are classified as :
1. Autotrophs can synthesise all theirorganic compounds by utilising atmosphericCO2& N2. No medical importance.
2. Heterotrophs unable to synthesise theirown metabolites & depend on preformedorganic compounds.
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Growth Factors
Some bacteria require certain organiccompounds in minute quantities Growth
Factors OR Bacterial Vitamins. It can be :
1. Essentialwhen growth does not occur intheir absence.
2. Accessory when they enhance growth,without being absolutely necessary for it.
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Growth Factors
Identical with mammalian nutrition
Vitamin B complex
1. thiamine2. riboflavine
3. nicotinic acid
4. pyridoxine5. folic acid &
6. Vit.B 12